The present invention relates to organopolysiloxane emulsifiers, and mineral oil solutions thereof, which are useful for preparing aqueous skin care emulsions and to skin care emulsions comprising said organopolysiloxane emulsifiers and a water-containing phase dispersed in a mineral oil-containing phase.
Skin care emulsions comprising water and mineral oil are valuable compositions because of the well known salutary skin-moisturizing and skin-softening effects that are obtained when such emulsions are applied to the skin. Of course, skin care emulsions typically further comprise other components, such as odorants; efficacious components, such as emollients, humectants, barrier agents and healing agents; and stabilizing agents, such as emulsifiers and preservatives to enhance the efficacy and customer acceptance of said emulsions.
Skin care emulsions comprising water and mineral oil are typically oil-in-water type emulsions instead of water-in-oil type emulsions, a situation which is at least partially due to a relative abundance of cosmetically acceptable emulsifiers for the former type and a relative shortage of cosmetically acceptable emulsifiers for the latter type.
However, water-in-mineral oil skin care emulsions are highly desirable because of the pleasant dry feel that one receives when such an emulsion is applied to one's skin, an effect not available from oil-in-water emulsions. Furthermore, since water-in-oil emulsions are not readily miscible with water they are valued as water-resistant skin care compositions. At least for these reasons, considerable effort has been devoted to the search for new emulsifiers that will provide water-in-mineral oil emulsions.
Starch, U.S. Pat. No. 4,311,695, discloses personal care creams and lotions of the water-in-oil type wherein the oil comprises a volatile component and a personal care component dissolved therein. Mineral oil is disclosed by Starch as a suitable personal care component. However, because of the particular organopolysilioxane emulsifier that is used by Starch the personal care composition must contain a water-soluble alcohol such as ethanol, isopropanol, propylene glycol or glycerol. The emulsifier that is used by Starch is an organopolysiloxane-polyoxyalkylene block copolymer wherein at least 95 percent of the organic radicals in the organopolysiloxane block are the methyl radical and the balance are ethyl, vinyl, phenyl and an alkylene radical linking the polyoxyalkylene block to the organopolysiloxane block, and the weight ratio of organosiloxane blocks to polyoxyalkylene blocks is equal to from 2/1 to 8/1.
U.K. Pat. No. 1,221,156 discloses a water-in-oil ointment base wherein the oil is an organosiloxane-oxyalkylene block copolymer and further teaches the desirability of bonding the oxyalkylene block of the block copolymer to the organosiloxane block by way of a hydrolytically stable silicon-carbon bond. Although the ointment base can further comprise adjuvants such as a scent, a pigment, a filler or white petroleum jelly, compositions comprising mineral oil or a water-in-mineral oil emulsion are not contemplated therein. The organopolysiloxane-oxyalkylene block copolymer recited in this patent contains only methyl radicals and alkylene-linked oxyalkylene radicals with the latter accounting for from 10 to 35 percent by weight of the block copolymers.
U.K. Pat. No. 1,041,341 relates to water-hydrocarbon systems which can be either oil-in-water emulsion systems or water-in-oil emulsion systems, depending upon which component is the major component. The emulsifier that is used in these systems is an organopolysiloxane-polyoxyalkylene block copolymer wherein the polyoxyalkylene blocks account for from 50 to 95 percent by weight of the block copolymer.
It is evident to one having knowledge of the skin care formulation art and of the emulsions art that there is a paucity of emulsifiers that are suitable for forming water-in-mineral oil emulsions that demonstrate stability to separation.
Although the above-noted patents relate to water-in-oil emulsion compositions their failure to disclose water-in-mineral oil compositions is understandable in view of the present invention. That is to say, the organopolysiloxane-oxyalkylene emulsifiers that are used in compositions of the above-noted references are ineffective to emulsify water-in-mineral oil because they contain excessive oxyalkylene portions and/or excessive methylsiloxane portions, unlike the organopolysiloxanes of the present invention.